This research project is investigating the cause, and treatment of infections of prosthetic heart valves. The bacterium, Staphylococcus epidermidis, has been used as the focus of this study because it is the most common organism causing prosthetic valve endocarditis. During the first year of this study 17 S.epidermidis isolates from patients with prosthetic valve endocarditis have been studied for antibiotic susceptibility, including the incidence of mutation to resistance and the kinetics of antimicrobial killing. The bactericidal effect of antibiotic combinations has also been investigated. Forty-one patients getting prosthetic valves have been followed prospectively with only one cause of endocarditis occuring. S. epidermidis isolates from these patients have been phage and biotyped and evaluated for antimicrobial susceptibility. An experimental model of S. epidermidis endocarditis has been devised in rabbits and various pathogenetic mechanisms have been investigated. The prospective study of patients getting prosthetic valves and the epidemiology of S. epidermidis are continuing. Investigations of the antigenic and pathogenic characteristics of S. epidermidis isolate and the mechanisms of antibiotic resistance are also currently in progress.